Semiconductor device and method for forming the same

ABSTRACT

A semiconductor device includes a semiconductor substrate with an active region, an oxide film that covers the active region of the semiconductor substrate, a first borophosphosilicate glass film that covers the oxide film, and a second borophosphosilicate glass film that covers the first insulating film. The first borophosphosilicate glass film has a boron concentration which is lower than that of the second borophosphosilicate glass film, and thus prevents out diffusion of phosphorus from the second borophosphosilicate glass film to the semiconductor substrate.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to a semiconductor device and a method for forming the same, and more particularly, the present invention relates to the semiconductor device and the method for forming the same, having a borophosphosilicate glass film as an interlayer insulator.

This application is a counterpart of Japanese application Serial Number 155220/1998, filed May 20, 1998, the subject matter of which is incorporated herein by reference.

2. Description of the Related Art

In general, a multi-level interconnection is used effectively to provide the advantage of high integration. In the multi-level interconnection, an interlayer insulator is formed between interconnections. A borophosphosilicate glass film as the interlayer insulator is used for planarization in VLSI circuit.

The borophosphosilicate glass film covers an active region of a semiconductor device such as a MOS transistor. After then, the borophosphosilicate glass film is reflowed using thermal treatment. As a result, the interlayer insulator having a smooth surface is formed.

However, phosphorus in the borophosphosilicate glass film is diffused to the active region of the semiconductor device during reflow. It is desirable to avoid the outdiffusion of the phosphorus to the active region of the semiconductor device.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a semiconductor device that can give an outdiffusion preventing function to an underlayer for phosphorus, of plural interlayer insulators including boron.

According to one aspect of the present invention, for achieving the above object, there is provided a semiconductor device comprising: a semiconductor substrate with an active region; an oxide film to cover the active region of the semiconductor substrate; a first borophosphosilicate glass film to cover the oxide film; and a second borophosphosilicate glass film to cover the first borophosphosilicate glass film; wherein the first borophosphosilicate glass film has a concentration of boron which is lower than that of the second borophosphosilicate glass film.

An object of the present invention is to provide a method for forming a semiconductor device that can avoid the outdiffusion of the phosphorus to the active region of the semiconductor device.

According to another aspect of the present invention, for achieving the above object, there is provided a method for forming a semiconductor device comprising:

providing a semiconductor substrate with an active region; covering the active region of the semiconductor substrate with an oxide film; covering the oxide film with a first borophosphosilicate glass film having an inhibitory of an outdiffusion of the phosphorus; covering the first borophosphosilicate glass film with a second borophosphosilicate glass film including a phosphorus and boron; and reflowing the second borophosphosilicate glass film so as to have a fluidity with thermal treatment.

BRIEF DESCRIPTION OF THE DRAWINGS

While the specification concludes with claims particularly pointing out and distinctly claiming the subject matter that is regarded as the invention, the invention, along with the objects, features, and advantages thereof, will be better understood from the following description taken in connection with the accompanying drawings, in which:

FIG. 1A-FIG. 1D are sectional views showing a method for forming a semiconductor device according to a first preferred embodiment of a present invention.

FIG. 2 is a sectional view showing a method for forming a semiconductor device according to a second preferred embodiment of a present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A semiconductor device according to first and second preferred embodiments of the present invention will hereinafter be described in detail with reference to the accompanying drawings.

FIG. 1A-FIG. 1D are sectional views showing a method for forming a semiconductor device according to a first preferred embodiment of a present invention. Here, for example, the semiconductor device a is DRAM (Dynamic Random Access Memory) having a COB(Capacitor On Bit line) structure.

As shown in FIG. 1A, a field oxide film 11, preferably to a thickness of about 400 nm, is formed on a surface of a semiconductor substrate 10 as a silicon, using LOCOS (LOCal Oxidation of Silicon) method. The field oxide film 11 serves as an isolation between transistors. By forming the field oxide film 11 on the surface of the semiconductor substrate 10, an active region is defined on the surface of the semiconductor substrate 10. A gate oxide film 13, preferably to a thickness of 50-150 Å, is formed on the active region of a semiconductor substrate 10. A gate 14, preferably to a thickness of 2000-4000 Å, is made up of a polysilicon layer 15 and a tungsten silicide layer 16. An insulating layer 17, preferably to a thickness of 2000-3000 Å, is made up of an NSG (Non doped Silicate Glass) film or a PSG (Phosphorus doped Silicate Glass) film formed on the gate 14 using CVD techniques. A sidewall spacer 18 is made up of an NSG film or a PSG film formed on a sidewall of the gate 14. A diffused region 19 is formed on the active region between gates 14 using ion-implantation technique. An oxide film 20, preferably to a thickness of 200-500 Å, is formed on the active region to avoid damages of the active region before the ion implantation. In a DRAM, a select transistor and a memory cell capacitor are formed on the active region 12 between gates 14.

As shown in FIG. 1B, a silicon nitride film is deposited using low pressure chemical vapor deposition and then the silicon nitride film is patterned so as to cover the gate 14, the sidewall spacer 18 and the oxide film 20 on the active region. As a result, the patterned silicon nitride serves as a sacrificial film 21. The sacrificial film 21 is formed on a region which forms a bit contact. A first borophosphosilicate glass film 22, preferably to a thickness of 1000-2000 Å, is formed on the sacrificial film 21 and on portions of the structure corresponding to exposed and removed portions of the silicon nitride film used to form sacrificial film 21, using CVD method. The first borophosphosilicate glass film 22 serves as a first interlayer insulator. A concentrator of a boron oxide in the first borophosphosilicate glass film 22 is 10-12 weight %. A concentration of phosphorus (P2O5) in the first borophosphosilicate glass film 22 is 10-15 weight %.

A second borophosphosilicate glass film 23, preferably to a thickness of 3000-5000 Å, is formed on the first borophosphosilicate glass film 22 using CVD method. The second borophosphosilicate glass film 23 serves as a second interlayer insulator. A concentration of a boron oxide in the second borophosphosilicate glass film 23 is 12-18 weight % which is higher than that of the first borophosphosilicate glass film 22. A concentration of phosphorus (P2O5) in the second borophosphosilicate glass film 23 is 10-15 weight % which is substantially same as that of the first borophosphosilicate glass film 22.

After depositing the first and second borophosphosilicate glass films 22, 23, the entire structure is annealed for reflow in N2 atmosphere at 800-950° C. As a result, a surface of the second borophosphosilicate glass film 23 become smooth. During this time, phosphorus in the first and second borophosphosilicate glass films 22, 23 tend to diffuse to the diffused regions 19 under the first and second borophosphosilicate glass films 22, 23 via the oxide film 20. However, the first preferred embodiment has the interlayer insulators of two layers which is made up of the first and second borophosphosilicate glass films 22, 23. Further, the first borophosphosilicate glass film 22 directly covering the oxide film 20 on the active region 12, has the concentration of the boron oxide which is lower than the second borophosphosilicate glass film 23. In a borophosphosilicate glass film including phosphorus and boron, it is well known that diffusion coefficient of the phosphorus is in proportion to the concentration of the boron. Therefore, the phosphorus diffusion coefficient of the first borophosphosilicate glass film 22 having the concentration of the boron which is lower than the concentration of the boron in the second borophosphosilicate glass film 23, is smaller than that of the second borophosphosilicate glass film 23. Accordingly, the first interlayer insulator 22 located between the second interlayer insulator 23 and the oxide film 20, serves as a phosphorus diffusion preventing film against the second interlayer insulator 23. By forming the first interlayer insulator 22 as the phosphorus diffusion preventing film, it can prevent diffusion from the second borophosphosilicate glass film 23 to the active region 12 via the oxide film 20. Accordingly, a contamination of the active region 12 caused by the phosphorus, can be avoided.

As shown in FIG. 1C, after a reflow treatment of the first and second borophosphosilicate glass films 22, 23, a contact hole 24 is formed in the first and second borophosphosilicate glass films 22, 23 which is not covered with the sacrificial film 21 and which locates on the diffused region 19, using a well-known photolithography and etching techniques. In etching for forming the contact hole, C4F8 gas is used. As a result, etch rate of the borophosphosilicate glass film increases with decrease of the concentration of boron.

Therefore, a phenomenon of etching stop easily appears in the first borophosphosilicate glass films 22, but the first borophosphosilicate glass films 22 has the etch rate which is larger than the second borophosphosilicate glass films 23. Accordingly, the contact hole 24 can preferably be formed.

After forming the contact hole 24, a bit line 25 is formed so as to contact to the diffused region 19 via the contact hole 24. After then, as shown in FIG. 1D, an interlayer insulator 26 is formed on the bit line 25. The interlayer insulator 26 is formed using the similar manner for the second borophosphosilicate glass films 23.

After forming the interlayer insulator 26, for forming a memory capacitor, a cell contact 27 is formed in the interlayer insulator 26, the first and second borophosphosilicate glass films 22, 23, and the sacrificial film 21, using first and second dry etching.

Next, a storage electrode 28 which is made up of a doped-polysilicon, is formed in the cell contact 27. A dielectric film 29 is formed on the storage electrode 28. A cell plate 30 is formed on the dielectric film 29. As a result, the memory capacitor is made up of the storage electrode 28, the dielectric film 29, and the cell plate 30.

In the dry etching, since the first borophosphosilicate glass film 22 has a concentration of boron oxide which is lower than the second borophosphosilicate glass film 23, the first borophosphosilicate glass film 22 has an etch rate which is higher than the second borophosphosilicate glass film 23. Therefore, before erosion of a shoulder portion 21 b of the sacrificial film 21 in the first dry etching, a bottom portion 21 a of the sacrificial film 21 can exposed. Accordingly, a damage of the sidewall spacer 18 in the second dry etching caused by the erosion of the shoulder portion 21 b of the sacrificial film 21, can be avoided. It can thus be avoided that the gate 14 shorts with the storage electrode 28. Further, the first preferred embodiment provides an underlayer having an outdiffusion preventing function for phosphorus of plural interlayer insulators that include boron.

FIG. 2 is a sectional view showing a semiconductor device according to a second preferred embodiment of a present invention.

As shown in FIG. 2, a field oxide film 11 is formed so as to surround a diffused region 19 on a semiconductor substrate 10. An oxide film 20 is formed on the diffused region 19. The oxide film 20 is covered with a first borophosphosilicate glass film 22. A second borophosphosilicate glass film 23 is formed on the first borophosphosilicate glass film 22. A cell plate 30 is formed on the second borophosphosilicate glass film 23. An interlayer insulator 26, preferably to a thickness of 4000-8000 Å, covers the cell plate 30. In a first contact hole 33 to the cell plate 30 via the interlayer insulator 26 a cell plate contact 31 is formed. In a second contact hole 34 to the diffused region 19 via the interlayer insulator 26, the first and second borophosphosilicate glass films 22, 23, and the oxide film 20, a diffused region contact 32 is formed. The first contact hole 33 has a different depth than the second contact hole 34. The first borophosphosilicate glass film 22 has an etch rate which is faster than the second borophosphosilicate glass film 23. Accordingly, the first and second contact holes having a different depth can form, simultaneously, without damaging the cell plate.

While the present invention has been described with reference to the illustrative embodiments, this description is not intended to be construed in a limiting sense. Various modifications of the illustrative embodiments, as well as other embodiments of the invention, will be apparent to those skilled in the art on reference to this description. It is therefore contemplated that the appended claims will cover any such modifications or embodiments as fall within the true scope of the invention. 

What is claimed is:
 1. A semiconductor device comprising: a semiconductor substrate having an active region; an oxide film that covers the active region of the semiconductor substrate; a first borophosphosilicate glass film that covers the oxide film; and a second borophosphosilicate glass film formed directly on the first borophosphosilicate glass film so as to be in contact with the first borophosphosilicate glass film, the second borophosphosilicate glass film having a concentration of boron oxide which is higher than a concentration of boron oxide in the first borophosphosilicate glass film and the second borophosphosilicate glass film having a concentration of phosphorus which is substantially the same as a concentration of phosphorus in the first borophosphosilicate glass film, to prevent out diffusion of dopants from the second borophosphosilicate glass film to the semiconductor substrate via the oxide film.
 2. The semiconductor device as claimed in claim 1, wherein the concentration of boron oxide in the first borophosphosilicate glass film is 10-12 weight % and the concentration of boron oxide in the second borophosphosilicate glass film is 12-18 weight %.
 3. The semiconductor device as claim in claim 1, wherein the oxide film has a thickness in a range of 200-500 Å.
 4. The semiconductor device as claimed in claim 3, wherein the first borophosphosilicate glass film has a thickness in a range of 1,000-2,000 Å and the second borophosphosilicate glass film has a thickness in a range of 3,000-5,000 Å.
 5. The semiconductor device as claim in claim 1, wherein the dopants comprise phosphorus.
 6. A semiconductor device comprising: a semiconductor substrate having an active region; an oxide film that covers the active region of the semiconductor substrate, the oxide film having a thickness in a range of 200-500 Å; a first borophosphosilicate glass film that covers the oxide film, the first borophosphosilicate glass film having a thickness in a range of 1,000-2,000 Å; and a second borophosphosilicate glass film formed directly on the first borophosphosilicate glass film so as to be in contact with the first borophosphosilicate glass film, the second borophosphosilicate glass film having a thickness in a range of 3,000 to 5,000 Å, the second borophosphosilicate glass film having a concentration of boron oxide which is higher than a concentration of boron oxide in the first borophosphosilicate glass film and the second borophosphosilicate glass film having a concentration of phosphorus which is substantially the same as a concentration of phosphorus in the first borophosphosilicate glass film.
 7. The semiconductor device as claimed in claim 6, wherein the concentration of boron oxide in the first borophosphosilicate glass film is 10-12 weight % and the concentration of boron oxide in the second borophosphosilicate glass film is 12-18 weight %.
 8. The semiconductor device of claim 6, wherein the concentration of boron oxide in the second borophosphosilicate glass film prevents dopants from diffusing from the first borophosphosilicate glass film to the semiconductor substrate via the oxide film, the dopants comprising phosphorus. 